Extended Abstract (124K)7.17
Spatial Variations of Surface Temperatures and Heat Fluxes over Lake Michigan
David A. R. Kristovich, ISWS and Univ. of Illinois, Champaign, IL; and M. C. Peters and M. S. Timlin
Spatial variations in surface water temperature have an important impact on the development of clouds in convective boundary layers induced by the Great Lakes in winter. However, the influence of these variations on atmospheric mesoscale boundary layer circulations is not well understood. The ultimate goal of this research is to investigate the influences of lake surface temperature variations on mesoscale atmospheric circulations in winter lake-effect environments. This presentation will give results of the first step toward this goal; comparison of satellite and aircraft-observed lake water surface temperatures and aircraft in situ observations of surface heat fluxes.
Satellite-derived analyses of lake surface temperature distributions, provided by the Great Lakes CoastWatch program, are the best available operational dataset of water temperature variations. However, frequent cloudiness over the Great Lakes region in winter can result in long time periods where satellite estimates of lake temperature are not available for large portions of the lake. This, in turn, can result in derived temperature analyses of the Great Lakes that are not representative of actual water temperature distributions. This can potentially produce significant uncertainty in the results of investigations of mesoscale atmospheric circulations. This presentation will outline initial results of two efforts: 1) comparison of lake surface temperature analyses derived from AVHRR satellite observations with those obtained by low-flying aircraft during the Lake-Induced Convection Experiment (Lake-ICE) and 2) examination of the influence of the lake surface temperature variations on variations of surface heat and moisture fluxes.
Criteria for inclusion of the aircraft data in these analyses included: 1) The aircraft was flying below 250 m above the lake, 2) the roll and pitch angles of the aircraft were less than 3.5°, 3) in situ instrumentation did not detect more than 50 cm-3 cloud particles (FSSP). Overall, satellite- and aircraft-derived temperatures tended to agree within about 3°C. However, the temperature biases tended to be spatially coherent on size scales of 10s of km, which may impact mesoscale atmospheric circulations induced by these surface temperature variations. On days with weak lake-effect forcing these variations can result in lake-air temperature difference errors of 30 to 50%.
Aircraft observations revealed striking mesoscale variations in heat fluxes. Lake-air temperature differences and vapor content differences tended to decrease eastward and southward across Lake Michigan, as anticipated in lake-effect snow events. However, there was considerable mesoscale variability in these quantities. Sensible heat fluxes, derived using eddy-correlation techniques, tended to decrease eastward and southward, but with considerable small-scale variability. Somewhat surprisingly, latent heat fluxes showed little evidence of spatial tendency over the lake, but exhibited considerable small-scale variability.
Session 7, Air-Sea Interaction Studies Using Satellite Observations
Tuesday, 15 May 2001, 9:00 AM-3:15 PM
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